In a manufacturing process of MEMS (Micro Electro Mechanical System) devices, a plasma etching processing is performed in order to form holes or grooves on a target object such as a silicon substrate. In a MEMS processing, the diameters of holes or the widths of grooves that are formed by the plasma etching may be greater than 100 μm, and thus the sizes of the openings of a mask pattern become large accordingly. Therefore, the area ratio of the openings (opening ratio) that take up the area of the target object is increased.
In order to perform a plasma etching on the target object which has an opening pattern with large openings and large opening ratio, performing a high-rate etching is required in comparison with an etching that is performed in semiconductor manufacturing processes. With respect to a high-rate etching to silicon, there is suggested a method for realizing a high-rate silicon etching on the target object that has the opening pattern whose the sizes of the openings are from 5 μm to 200 μm by controlling the distance between a plasma generating portion and the target object, preferably, equal to or less than 20 μm, and setting a gas pressure in a processing chamber to be in the range from 13 Pa to 1,333 Pa (for example, see Japanese Patent Laid-open Publication NO. 2002-93776, claims 1 and 3 etc.).
In general, the etching rate is desirable to be high in order to enhance the throughput. Especially, since etching the target object which has an opening pattern with large openings and large opening ratio is performed in the MEMS processing, the above-described high-rate etching is needed.
However, when the high-rate etching is performed on the target object which has the opening pattern with the large openings whose size gets large to be equal to or greater than 500 μm, etching nonuniformity occurs on the surface of the target object. Specifically, when a central portion is compared with a peripheral portion on the surface of the target object, the etching rate at the peripheral portion is higher than that at the central portion. As a result, an etching amount at the peripheral portion is greater than that at the central portion. Therefore, there is a problem that the depths of the holes or grooves are not uniform on the surface of target object.